A Small-Size Dual-Feed Broadband Circularly Polarized U-Slot Patch Antenna

A small-size broadband circularly polarized U-slot patch antenna with dual-feed is proposed. By introducing an additional feeding probe near the vertical slot of the conventional singly fed square U-slot patch antenna printed on a high-permittivity substrate, two series resonances in close proximity are excited. The two resonant frequencies are found to be independent of the orientation of U-slot with respect to the patch, and broadband circular polarization is achieved by introducing a nonquadrature phase difference between two feeding ports. Experimental results show that the overlapped bandwidth of VSWR ≤ 1.5 and AR ≤ 3 dB is over 20% with a small overall size of 0.33λ
₀
× 0.33λ
₀
× 0.068λ
₀
, where λ
₀
is the free-space wavelength at the center frequency within the operating band.